Testing magnetic cores and coils



Sept. 10, 1 E. PETERSON TESTING MAGNETIC CORES AND COIIJ' S Filed April21 OVER COMPEWSATED TRUE LOOP N0 COUPE/VS TION wvnvrok E. PETERSONATTORNEY Patented Sept. 10, 1940 2,214,625 TESTING MAGNETIC CORES ANDGOILS Eugene Peterson, New York, N.

Bell Telephone Laboratories,

Y., assignor to Incorporated,

New York, N. Y., a corporation of New York Application April 21, 1939,Serial No. 269,084 3Claims. (01.175-183) This invention relates totesting and measuring the properties of magnetic materials and thecharacteristics of coils wound upon cores of magnetic materials.

In accordance with this invention, the ma netizing current of a coil tobe tested or wound upon the magnetic material to be tested is employedto deflect the cathode ray of a cathode ray oscillograph in a horizontaldirection while the voltage appearing across the coil is employed todeflect the cathode ray in a vertical direction. Thus, the spot willtrace a figure on the screen of a cathode ray oscillograph resemblingthe hysteresis loop of the material.

In all of the arrangements of the prior art which employ a cathode rayoscillograph to trace the hysteresis loop of magnetic material, two

windings are required to be wound upon the magnetic material, onewinding being employed to magnetize the material and the other windingto measure the flux or change of flux through the material. Thus,certain coils provided with only one winding, such as certain saturablecoils employed in harmonic producers, cannot be readily tested by any ofthe arrangements disclosed in the prior art, such as in U. S. Patents1,574,350, Johnson, February 23, 1926; 2,010,189, Hallowell, Jr., August6, 1935; and 2,035,248, Scott, March 24, 1936.

It is, accordingly, an object of this invention to provide anarrangement for obtaining a hysteresis loop of magnetic materialprovided with only one winding.

When it was attempted to obtain a hysteresis loop by controlling thehorizontal deflection of the cathode ray by'the current flowing throughthe coil and in the vertical direction by the voltage between theterminals of the coil, it was discovered that the figure obtained didnot represent a true hysteresis loop of the coil or of the mag- It wasdiscovered that an addinetic material. tional voltage component due tothe resistance drop across the coil occasioned by the magnetizingcurrent flowing through the resistance of the winding was included'inthe voltage causing the vertical deflection of the cathode ray. Wherethe magnetizing current is large, as, for example, in the 'case" wherethe magnetic material is saturated as in harmonic producers, thisadditional voltage becomes sufficiently large to cause the figure tracedupon the screen of the cathode ray oscillograph to materially departfrom the true hysteresis loop of magnetic material.

Another object of this invention is to provide an arrangement forneutralizing, balancing or canceling the effects of this additionalvoltage in deflecting the spot vertically so that a true hysteresis loopof the material of the core of the single wound coil may be obtained. I

Another object of this invention is to provide an arrangement wherebythe iron loss and the copper loss of a single wound coil may be readilydetermined and measured.

The testing system in accordance with this invention has been discoveredto be particularly well suited for the rapid testing of single woundcoils having cores of magnetic materials. If any of the turns of thecoil are short-circuited or there are any other substantialirregularities in the winding of the coil, they will materially affectthe shape of the hysteresis loop, thus permitting these irregularitiesto be readily detected.

It is, therefore, another object of this invention to provide anarrangement for rapidly measuring the characteristics of single woundcoils.

The foregoing objects and other objects and features of this invention,the novel features of which are set forth in the claims appended hereto, may be more fully understood from the following description whenread with reference to the attached drawing in which:

Fig. 1 shows a circuit arrangement employed for testing and measuringmagnetic properties, magnetic materials and the characteristics of coilswound upon cores of such materials; and

Fig. 2 shows a series of hysteresis loops showing the effects ofchanging the adjustment of the circuit to provide different degrees ofcompensation.

Briefly the magnetic material to be tested is 88 provided with a singlewinding. An alternating current is caused to flow through this windingand the magnitude of this current caused to control the horizontaldeflection of a cathode oscillograph tube. The potential difference be-40 tween the terminals of the coil due to the alternating currentflowing through the coil is applied to the cathode ray oscillograph tubeso as to deflect the cathode ray in a vertical direction. Thus the spoton the screen of the tube will 4 trace the hyseresis loop of themagnetic material comprising the core of the single wound coil.

In order to compensateor counteract the voltage drop appearing acrossthe coil due to the alternating current flowing through the resistanceof 5.

'the winding of the coil an auxiliary transformer is employed having aresistance connected across its primary winding and the parallelcombination of the resistance and primary winding of the transformerconnected in series with said single .beam or ray of electrons.

age appearing across the winding or .width of the loop is primarilywound coil so that the magnetizing current of the coil flows throughthis combination. The secondary winding of the auxiliary transformer isconnected in series with the voltage employed to control the verticaldeflection of the cathode ray beam. This additional voltage is adjustedto have substantially the same magnitude but opposite phase to theresistance drop due to the magnetizing current ance of the singlewinding wound upon the magnetic material or coil under test.

Referring now to Fig? 1, l0 represents a cathode ray oscillograph tubeprovided with an electron emitting cathode II, which may be'heated fromany suitable source of power such as battery 28, and beam forming,focussing and accelerating electrodes l2 and I3. These electrodes aremaintained at suitable potentials from any suitable source of power suchas battery 21 and potentiometer 26.

The tube was well as the elements l2 and 3 and the associated sources ofpotential shown in the drawing are merely intended to represent aconventional cathode ray oscillograph tube with an electron gun suitablefor producing a Any cathode ray tube having some means for forming abeam of electrons and directing said beam to a target or screen of moreor less elements than shown in the drawing, and the associated circuitswill be equally satisfactory to form part of the present invention asmay be well understood by those skilled in the art.

The magnetic material or core I! under test is provided with a singlewinding l8. The winding 8 is connected to a source of alternatingcurrent 24 through current regulating resistance 23 and the resonantnetwork 25. Resonant network 25 is employed to permit suflicient currentof the frequency of source 24 ing l8 and at the same time preventssource 24 from short-circuiting or shunting coil I8 at otherfrequencies. The voltage drop across the current regulating resistance23 is applied to the horizontal deflecting plates l5 and cathode rayoscillograph tube l0 and causes the electron beam and the spot at whichit strikes screen 33 to be-deflected in a.horizontal direction inaccordance with the instantaneous value of the current flowing throughresistance 23. The voltcoil I8 is applied to the vertical deflectingplates ll of the cathode ray oscillograph tube l0 through amplifier Hi.It is to be understood that a similar amplifier may be connected betweenthe resistance 23 and the horizontal deflecting plates l5 when it isrequired. It is to be also understood that amplifier l6 may :bedispensed with when the voltage across the coil I8 is of sufficientmagnitude to give a satisfactory deflection without amplification. Y

Curve 29 of Fig. 2 shows a typical hysteresis loop of a single woundcoil when the auxiliary transformer I9 is shorf-circuited. This loop isbroader than the actual magnetic material of core H. The additional dueto the fact that its area represents both the copper loss caused by themagnetizing current flowing through the resistance of winding l8 and thecore loss due to the hysteresis and eddy current losses in the magneticmaterial I1.

In order to obtain a true hysteresis loop with the magnetic material I!an auxiliary transformer l9 having a primary winding 2| anda flowingthrough the resistto iiow through wind hysteresis loop of the 1 winding20 of transformer is so connected with respect Fig. 1.

secondary winding 20 is connected as shown in A variable resistance 22is connected in parallel with the primary winding 2| of transformer l9and'this parallel combination is connected in series with coil l8 andthe source of alternating current 24. Thus the magnetizing current forcoil l3 flows through this parallel combination of resistance 22 andprimary winding transformer 2|. Transformer l9 operates at a very lowflux density and its primary impedance is very much higher than theimpedance of resistance 22 across which it is connected. Thus thevoltage drop across the parallel combination of resistance 22 in theprimary winding- 2| of transformer l9 will be substantially in phasewith the magnetizing current flowing through coil 8 and substantially inphase with the resistance drop across-the winding l8 due to magnetizingcurrent flowing through the resistance of this coil. r v

The secondary winding 20 of transformer I8 is connected in series withthe voltage developed across the coil l8 and the combined voltage isapplied to the vertical deflecting plates i4 through amplifier I6. Sincethe voltage across the primary winding 22 oftransformer I9 issubstantially in phase coil 8 the voltage appearing across the secondaryl9 will also be substantially in phase or in phase opposition, i. e.,degrees out of phase with the resistance drop appearing across windingIS. The winding 20 to coil l8 that the voltage appearing across winding20 is in substantial phase opposition to the resistance drop due to themagnetizing current flowing through the resistance of winding |8. Bysuitably adjusting the value or magnitude of resistance 22 the voltageacross the secondary winding 20 of transformer I! may be made equal inmagnitude to the resistance voltage drop across the single winding |8 oncore I! and thus substantially neutralizing or balance out this voltage,due to the magnetizing current flowing through the resistance of coill8.

Curve 30 of Fig. 2 shows a typical hysteresis of resistance 22 is Ifresistance 22 is increased so that the magnitude of the voltage acrosswinding 20 exceeds the voltage drop across coil I8 due to themagnetizing current flowing through the resistance of its. winding, anover-compensated hysteresis loop such as shown by curve 3| of Fig. 2 isobtained clearly indicating that resistance 22 is too high.

This arrangement lends itself particularly well to of any coil ortransformer because the product of the square of the magnetizing currentand thevalue of resistance 22 when it is properly adjusted, as describedabove so that substantially a true hysteresis loop is traced upon thescreen 33 of the cathode ray oscillograph tube l0, represents the copperloss of coil I! under the operating conditions under which it is tested.The area with the resistance drop across separating the copper loss fromthe core loss aci osis harmonic producers and other circuits in whichthe coil is operated at high ilux densities or in which the saturatingproperties of the magnetic material are made use of. Any irregularitiesin the winding it such as short-circuited tur'ns, high distributedcapacity, etc., materially aiiect the size and shape of the hysteresisloop. Consequently, it is only necessary to connect the two terminals ofthe coil winding to the circuit and observe the size and shape of thehysteresis loop to evaluate the properties of the coil and determinewhether or not it is suitable for certain uses or for use in certaincircuits.

It is to beunderstood that this invention is not limited to the specificembodiment set forth in the drawing and described above but includes anymodifications which will readily occur to those skilled in the art.

What is claimed is:

1. A testing arrangement comprising a cathode ray oscillograph tubeincluding a screen and means for producing and directing a beam ofelectrons toward said screen, a coil to be tested comprising a core anda single winding wound thereupon, means for causing current to flowthrough the winding of said coil, means for deflecting said beam ofelectrons parallel to an axis of said screen which deflections areproportional to the instantaneous current flowing through the winding ofsaid coil and means for. deflecting said beam of electrons parallel toan axis of said screen at right angles to said first axis whichdeflections are proportional to the potential dif-- ference between theterminals of the winding of said coil and means for applying anadditional potential difference to said last-mentioned means in serieswith the potential difference between the terminals of the winding ofsaid coil which additional potential difference is substantially equalto but opposite in phase to that portion of said first-mentionedpotential difference which is due to said current flowing through theresistance of said single winding of said coil.

2. A testing arrangement comprising a cathode ray oscillograph tubeincluding a screen, and means for producing and directing a beam ofelectrons toward said screen, a coil to be tested comprising a singlewinding, means for causing current to flow through said winding, meansfor deflecting said beam of electrons parallel to a line on said screenwhich deflections are proportional to the instantaneous current flowingthrough said single winding, and means for deflecting said beam parallelto another line on said screen at an angle to said first line whichdeflections are proportional to the instantaneous potential differencebetween the terminals of said winding and means for applying anadditional potential difference to said last-mentioned deflection meanswhich additional potential difference is substantially equal to but inphase opposition to that portion of the first-mentioned potentialdifference which is due to said current flowing through theresistance.of said winding.

3.-A testing arrangement for testing a coil having a single windingcomprising means for causing a current. to flow through said winding andmeans responsive to the instantaneous current flowing through saidwinding, other means responsive to the instantaneous potentialdifference across said winding and means for applying an additionalpotential difference to said lastmentioned responsive means whichadditional potential difference is substantially equal to but oppositein phase to the portion of the firstmentioned potential difference whichis in phase with the current flowing through said winding.

EUGENE PETERSON.

